Credit: The Associated Press

Attorney General Eric Holder, center, speaks during a news conference at the Justice Department, on Monday, May 19, 2014, in Washington. The Justice Department on Monday charged Credit Suisse AG with helping wealthy Americans avoid paying taxes through offshore accounts, and a person familiar with the matter said the European bank has agreed to pay about $2.6 billion in penalties. From left, Deputy Attorney General James Cole, Holder, Assistant Attorney General for the Tax Division Kathryn Keneally, and IRS Commissioner John Koskinen (AP Photo/ Evan Vucci)

WASHINGTON — Credit Suisse AG's guilty plea and $2.6 billion payment in a high-profile case brought by the Justice Department are being held out as a warning to foreign banks believed to be helping U.S. taxpayers conceal assets.

Culminating a yearslong criminal investigation, Switzerland's second-largest bank pleaded guilty Monday to helping wealthy Americans avoid paying taxes through secret offshore accounts. Credit Suisse was the largest bank to plead guilty in more than 20 years.